One of available methods for treating diseases such as malignant tumors is particle beam radiation therapy. Particle beam radiation therapy is a method for treating diseases by irradiating a malignant tumor or the like with particle beams, such as heavy particles, to kill cells in the malignant tumor or the like. Particle beam radiation therapy may cause damage to normal organs and the like around a malignant tumor or the like, because normal organs and the like around the malignant tumor or the like are also irradiated with the particle beams.
In particle beam radiation therapy, particle beams irradiated to a tumor can damage any gastrointestinal tract being present at a position in contact with the tumor, resulting in gastrointestinal perforation; and thus some arrangement is needed to avoid concentration of the particle beam radiation dose on the gastrointestinal tract by creating a space between the tumor and the gastrointestinal tract (intestinal tract). To reduce damage to gastrointestinal tracts caused by particle beams, a spacer is conventionally embedded between a tumor and a normal tissue.
FIG. 1 illustrates an example spacer embedded between a tumor and normal organs or the like in the body. According to the example in FIG. 1, a spacer is embedded between the tumor and the normal organs or the like. In addition, the tumor is irradiated with particle beams from outside the body. The size of the irradiation field, which is the area irradiated with particle beams, is to be greater than the size of the tumor. Embedding a spacer between the tumor and the normal organs or the like reduces irradiation of the normal organs or the like with particle beams, which are irradiated toward the tumor.